Trouble with Orbital Sander...

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  #1  
Old 06-08-05, 08:16 PM
depaulj
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Trouble with Orbital Sander...

Hello all -

I just bought a used 5inch Orbital Sander: Bosch 3107DVS - from a local pawn shop. The tool was made in Switzerland, it was in fairly good condition and when I plugged it in the store it ran strong and was well balanced, so I went for it.

When I brought it home and tested it on a piece of soft wood it started out strong without any load on it but as soon as I made contact with the wood, I noticed that it started losing power.

I took time to take it all apart - it was very dusty inside around the armature coils and the brushes, so I cleaned it well with my air compressor hoping that it will help with the power, but when I put it all together the loss of power was once again noticable...

I feel really disappointed with myself for making such a stupid purchase - but besides that, is there something a do-it-yourselfer could do to refurbish the motor and solve this power-loss problem?!

Thanks,
James
Denver, CO
 
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  #2  
Old 06-08-05, 08:56 PM
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Have you tried adjusting the dial on the switch that controls the variable speed? Perhaps it's on a slow setting.
 
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Old 06-09-05, 07:17 AM
depaulj
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Trouble with Orbital sander...

Originally Posted by XSleeper
Have you tried adjusting the dial on the switch that controls the variable speed? Perhaps it's on a slow setting.
Yes - I had it on "6" - the highest setting - power loss seems to occurs on all levels of the speed dial...

What are some common reasons for loss of speed on such tools - I've got to believe the motor is still good - it's a Bosch afterall...!
 
  #4  
Old 06-09-05, 07:32 AM
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My personal belief is that the overworked motor overheats and causes a short in the winding. This short effectively reduces the motor output, as if someone had removed the winding and installed a winding with half the original length.

The copper windings may look bare, but are actually insulated from one another with a thin coat of shellac (or similar coating). Hot spots can develop and burn away this super thin coating. When that happens, the current bypasses a part of the winding, thus reducing the power.

Of course it could be a weak on/off switch or stiff worn bearings.
 
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Old 06-09-05, 07:52 AM
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The power loss is only under load?
If you just plug it in it seems fine, and when actually using it, that's when you notice the power loss?
I don't know about random orbitals, but that would be typical of worn brushes a regular motor
 
  #6  
Old 06-09-05, 08:18 AM
depaulj
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Originally Posted by Lugnut
Of course it could be ... stiff worn bearings.
What is "stiff worn bearings" - I've noticed that the bearing that holds the shaft in place on top of the tool is rather loose (it seems it's pretty worn out) - would that cause excessive wobble and affect the brushes?! I've seen the brushes 'sparking' when I ran it while it was apart...

Again - under no load the tool seems very strong and it's only when I put it to some wood that it starts to fade...

Checking the brushes - they are worn but when I pull them out (spring loaded) they seem to have with plenty of materials left on them. Is it also possible that the brushes have material left but would still need replacement?!

James
 
  #7  
Old 06-09-05, 08:31 AM
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Excessive sparking is a sign of worn brushes. Can't comment on your brushes. Normally they are worn down to the point of falling out, but that is by no means a conclusive fact.

The good news is that Ace Hardware sells over a dozen sizes of brushes, all for a buck each or so. Take one with you to the store, match it up and buy it. If if don't fit exactly, then file it down till it fits. They are stored in the small parts drawers near the power tools so you will have to look for them.
 
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